SOLUTION: Solve the system by substitution. x + y = 12 y = 2x Again I need help with this problem. I also need help with showing how the problem is done step- by- step. Then maybe

Question 102507: Solve the system by substitution.
x + y = 12
y = 2x
Again I need help with this problem. I also need help with showing how the problem is done step- by- step. Then maybe I can actually figure out how to figure these things out by myself, please, and thank you!!
Answer by doukungfoo(195) (Show Source): You can put this solution on YOUR website!
x + y = 12
y = 2x
Ok we have a system of equations here. To solve by substitution we are going to use information from the second equation and substitute it into the first equation.
So here is the first equation:
x + y = 12
now since the 2nd equation tells us that y is equal to 2x let substitute that in
so
x + y = 12 becomes
x + 2x = 12
now we have an equation with only one variable to solve for
so lets solve it
x + 2x = 12
combine x and 2x to get 3x
3x = 12
divide both sides by 3
3x/3 = 12/3
x = 4
Answer: We found that x = 4
now use this value for x in ethier equation to solve for y
so lets use the 2nd equation
y = 2x
sub in 4 for the x
y = 2*4
y = 8
Answer: Now we found y = 8
Check both answers in both equations
1st equation:
x + y = 12
4 + 8 = 12
12 = 12
that works now try the 2nd equation
y = 2x
8 = 2*4
8 = 8
That works too. So now we can be sure that we have sucessfully solve the system of equations.

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